OpenAI: GPT-5.5 Pro vs SpaceXAI: Grok 4.20
Head-to-head API pricing and cost comparison between OpenAI’s OpenAI: GPT-5.5 Pro and xAI’s SpaceXAI: Grok 4.20. Prices auto-refresh daily from OpenRouter.
SpaceXAI: Grok 4.20 is 96% cheaper for input tokens; SpaceXAI: Grok 4.20 also wins on output tokens.
Side-by-side comparison
| Spec | OpenAI: GPT-5.5 Pro | SpaceXAI: Grok 4.20 |
|---|---|---|
| Input price (per 1M) | $30.00 | $1.25 |
| Cached input (per 1M) | — | $0.20 |
| Output price (per 1M) | $180.00 | $2.50 |
| Batch input (per 1M) | $15.00 | — |
| Batch output (per 1M) | $90.00 | — |
| Reasoning price (per 1M) | — | — |
| Context window | 1050K | 2000K |
| Vision support | Yes | Yes |
| Caching support | No | Yes |
| Batch API | Yes | No |
| Reasoning capability | No | No |
Monthly cost at volume
Estimated monthly API spend at common production traffic levels (input/output tokens per request shown).
| Volume | OpenAI: GPT-5.5 Pro | SpaceXAI: Grok 4.20 | Savings |
|---|---|---|---|
1K req/day 500in / 200out tokens | $1,530 | $33.75 | $1,496 SpaceXAI: Grok 4.20 wins |
10K req/day 1500in / 500out tokens | $40,500 | $937.50 | $39,563 SpaceXAI: Grok 4.20 wins |
100K req/day 3000in / 800out tokens | $702,000 | $17,250 | $684,750 SpaceXAI: Grok 4.20 wins |
1M req/day 8000in / 2000out tokens | $18,000,000 | $450,000 | $17,550,000 SpaceXAI: Grok 4.20 wins |
Adjust input/output token counts, request volume, batch & cached pricing.
Related comparisons
Frequently asked questions
Which is cheaper, OpenAI: GPT-5.5 Pro or SpaceXAI: Grok 4.20?
For input tokens, SpaceXAI: Grok 4.20 is roughly 96% cheaper at $1.25/1M vs $30.00/1M. For output tokens, SpaceXAI: Grok 4.20 wins at $2.50/1M. Real-world cost depends on your input/output ratio — use the calculator to model your actual workload.
What’s the context window difference?
OpenAI: GPT-5.5 Pro has a context window of 1050K tokens. SpaceXAI: Grok 4.20 offers 2000K tokens. Larger context windows are valuable for long documents, RAG pipelines, and multi-turn conversations — but they come with higher input-token bills if you fill them every request.
Should I use OpenAI: GPT-5.5 Pro or SpaceXAI: Grok 4.20?
Choose OpenAI: GPT-5.5 Pro if you’re already on the OpenAI stack, want broad ecosystem support, or prefer its feature set. Choose SpaceXAI: Grok 4.20 for xAI’s ecosystem, native vision input, or its cheaper input tokens. Run a small benchmark on your own prompts before committing — price is only one axis.
How are these prices kept current?
Prices are pulled directly from OpenRouter’s public models API once every 24 hours via a Convex cron job, then normalized to per-1M-token figures. Last refresh: Aug 7, 2026.